1. Field of the Invention
The present invention relates to the field of laser etching of target surfaces through ablation and methods for smoothing surfaces using lasers as well as targets modified by such ablative techniques.
2. Background
The use of laser beams to modify surfaces is known. In the early 1980's, it was discovered that pulsed lasers emitting in the ultraviolet frequency range could affect a target surface through ablative photodecomposition (APD). Later it was found that by using APD, layers of target material could be removed on the order of about one micron of target material per laser pulse.
It was further noted that APD did not significantly alter the characteristics of the newly exposed material immediately below the ablated material. This phenomenon has been explained as being due to the UV laser providing enough energy in a short enough period of time to actually break the covalent bonds of the polymeric target materials without heating the substrate. (See U.S. Pat. Nos. 4,417,948 and 4,568,632). Further scanning techniques using APD are disclosed in U.S. Pat. No. 5,061,342.
Certain materials, when ablated, create varying amounts of debris, some of which is redeposited upon the surface of the target material. It is believed that this redeposited debris somehow frustrates efforts to predictably modify the target surface using APD. Further, certain materials can not be as cleanly etched as others. A method for removing the deposited and adhered debris from the target surface while avoiding further debris accumulation is not known.